The Opposing Roles of IVS2+691 CC Genotype and AC/AG Diplotype of 118A>G and IVS2+691G>C of OPRM1 Polymorphisms in Cold Pain Tolerance Among Opioid-Dependent Malay Males on Methadone Therapy

Hyperalgesia in Patients With a History of Opioid Use Disorder: A Systematic Review and Meta-Analysis

Importance

Short-term and long-term opioid treatment have been associated with increased pain sensitivity (ie, opioid-induced hyperalgesia). Treatment of opioid use disorder (OUD) mainly involves maintenance with methadone and buprenorphine, and observations of heightened cold pain sensitivity among patients are often considered evidence of opioid-induced hyperalgesia.

Objective

To critically examine the evidence that hyperalgesia in patients with OUD is related to opioid use.

Data Sources

Web of Science, PubMed, and Embase between March 1, 2023, and April 12, 2024, were searched.

Study Selection

Studies assessing cold pressor test (CPT) pain responses during treatment seeking, pharmacological treatment, or abstinence in patients with OUD history were included.

Data Extraction and Synthesis

Multilevel random-effects models with robust variance estimation were used for all analyses. Study quality was rated with the JBI checklist. Funnel plots and Egger regression tests were used to assess reporting bias.

Main Outcomes and Measures

Main outcomes were pain threshold, tolerance, and intensity in patients and healthy controls, and unstandardized, standardized (Hedges g), and percentage differences (%Δ) in these measures between patients and controls. The association between pain sensitivity and opioid tolerance, withdrawal, and abstinence indices was tested with meta-regression.

Results

Thirty-nine studies (1385 patients, 741 controls) met the inclusion criteria. Most studies reported CPT data on patients undergoing opioid agonist treatment. These patients had a mean 2- to 3-seconds lower pain threshold (95% CI, -4 to -1; t test P = .01; %Δ, -22%; g = -0.5) and 29-seconds lower pain tolerance (95% CI, -39 to -18; t test P < .001; %Δ, -52%; g = -0.9) than controls. Egger tests suggested that these differences may be overestimated. There were some concerns of bias due to inadequate sample matching and participant dropout. Meta-regressions yielded no clear support for hyperalgesia being opioid related.

Conclusion and Relevance

Patients receiving opioid agonist treatment for OUD are hypersensitive to cold pain. It remains unclear whether hyperalgesia develops prior to, independent of, or as a result of long-term opioid treatment. Regardless, future studies should investigate the impact of hyperalgesia on patients' well-being and treatment outcomes.

OPRM1 rs2075572 has potential to affect plasma buprenorphine level in opioid users, but not OPRM1 rs562859

OPRM1 gene encoding mu-opioid receptor (MOR) is the primary candidate gene for buprenorphine (BUP) pharmacogenetics. OPRM1 undergoes alternative splicing leading to multiple MOR subtypes. Thus, in the current study 2 SNPs (rs1799972 and rs562859) were selected due to evidence for their contribution to alternative splicing of OPRM1. The effects of 2 SNPs of OPRM1 gene on plasma buprenorphine and norbuprenorphine levels in a sample of 233 OUD patients receiving BUP/naloxone were examined. Polymorphisms were analyzed by PCR and RFLP. BUP and norbuprenorphine concentrations in plasma were measured by LC-MS/MS. OPRM1 rs2075572 GC + CC (0.12 ng/ml) had significantly higher plasma BUP level compared to GG (0.084 ng/ml) (p = 0.043). Although there was not a statistically significant difference between OPRM1 rs562859 genotypes (p = 0.46), patients with OPRM1 rs562859 CT + TT had higher plasma BUP and BUP-related values as compared to those with CC. In conclusion, the effect of OPRM1 rs2075572 on BUP levels in opioid users' plasma was shown in a Caucasian population for the first time. On the other hand, OPRM1 rs562859 seems not to influence the BUP pharmacology.

Genetic Vulnerability to Opioid Addiction

Opioid addiction, also referred to as opioid use disorder, continues to be a devastating problem throughout the world. Familial relation and twin studies have revealed opioid addiction, like other addictive diseases, to be profoundly influenced by genetics. Genetics studies of opioid addiction have affirmed the importance of genetics contributors in susceptibility to develop opioid addiction, and also have important implications on treatment for opioid addiction. But the complexity of the interactions of multiple genetic variants across diverse genes, as well as substantial differences in allelic frequencies across populations, thus far limits the predictive value of individual genetics variants.

Influence of DRD2 Polymorphisms on the Clinical Outcomes of Opioiddependent Patients on Methadone Maintenance Therapy

Introduction:

Dopamine receptor D2 (DRD2) is one of the dopamine receptors that have been studied in relation to opioid dependence. It is possible, therefore, that DRD2 gene (DRD2) polymorphisms influence treatment outcomes of patients with opioid dependence. The objective of this study was to investigate the influence of DRD2 polymorphisms on the clinical outcomes of opioid-dependent patients on methadone maintenance therapy (MMT).

Materials and Methods:

Patients with opioid dependence (n = 148) were recruited from MMT clinics. Pain sensitivity, severity of the opiate withdrawal syndrome, and sleep quality were assessed using cold pressor test (CPT), Subjective Opiate Withdrawal Scale (SOWS-M), and Pittsburgh Sleep Quality Index (PSQI)-Malay, respectively. Deoxyribonucleic acid (DNA) was extracted from whole blood, and then was used for genotyping of Val96Ala, Leu141Leu, Val154Ile, Pro310Ser, Ser311Cys, TaqI A, -141C Ins/Del, and A-241G polymorphisms.

Results:

Among 148 patients, 8.1% (n = 12), 60.8% (n = 90), 27.7% (n = 41), and 29.1% (n = 43) had at least one risk allele for Ser311Cys, TaqI A, -141C Ins/Del, and A-241G polymorphisms, respectively. There were no significant differences in pain responses (pain threshold, tolerance, and intensity), SOWS, and PSQI scores between DRD2 polymorphisms.

Conclusion:

The common DRD2 polymorphisms are not associated with pain sensitivity, severity of the opiate withdrawal syndrome, and sleep quality in patients with opioid dependence on MMT. However, this may be unique for Malays. Additional research should focus on investigating these findings in larger samples and different ethnicity.

ABCB1 Polymorphisms and Cold Pressor Pain Responses: Opioid-Dependent Patients on Methadone Maintenance Therapy

BACKGROUND

Methadone is a substrate of the P-glycoprotein efflux transporter, which is encoded by ABCB1 (MDR1), and thus, ABCB1 polymorphisms may influence the transport of methadone at the blood-brain barrier, affecting its adverse effects.

OBJECTIVES

This study investigated the association between ABCB1 polymorphisms and cold pressor pain responses among opioid-dependent patients on methadone maintenance therapy (MMT).

METHODS

Malay male opioid-dependent patients receiving MMT (n = 148) were recruited. Cold pressor pain responses (pain threshold, pain tolerance, and pain intensity) were measured at 0, 2, 4, 8, 12, and 24 hours post-methadone dose. DNA was extracted from whole blood and genotyped for ABCB1 polymorphisms including 1236C>T (rs1128503), 2677G>T/A (rs2032582), and 3435C>T (rs1045642) using the allelic discrimination real-time polymerase chain reaction. Repeated-measure analysis of variance between-group analysis was used to compare the three cold pressor pain responses and ABCB1 polymorphisms (1236C>T, 2677G>T/A, and 3435C>T) according to genotypes and allelic additive models, genotype dominant and recessive models, haplotypes, and diplotypes.

RESULTS

Patients with 2677 GG or 2677G allele had the lowest pain threshold compared with 2677G>T/A genotypes or alleles (p = .007 and .002, respectively). Haplotype analysis showed a significant association between ABCB1 haplotypes and pain threshold (p = .02). Patients with 2677G allele had the lowest pain tolerance compared to those with 2677T and 2677A alleles (2677G < 2677T < 2677A allele carriers; p = .05). In terms of pain intensity scores, patients with 2677 GG or 2677G allele had the highest scores compared to other 2677G>T/A genotypes or alleles (p = .04 and .008, respectively). Haplotype analysis revealed a significant difference between patients with CGC haplotype and those without this haplotype (p = .02).

DISCUSSION

To the best of our knowledge, this study provides the first evidence that ABCB1 polymorphisms are associated with cold pressor pain responses among Malay male patients with opioid dependence on MMT. The results may provide an initial prediction on heightened pain sensitivity or hyperalgesia for individuals who are carriers of the ABCB1 polymorphisms.

Relationship between CYP2B6*6 and cold pressor pain sensitivity in opioid dependent patients on methadone maintenance therapy (MMT)

BACKGROUND

CYP2B6 polymorphisms contribute to inter-individual variations in pharmacokinetics of methadone. Increased pain sensitivity is frequently reported by opioid dependent patients on methadone maintenance therapy (MMT). It is possible, therefore, that genetic polymorphisms in CYP2B6, which affects the metabolism of methadone, influence pain sensitivity among patients on MMT. This study investigated CYP2B6 polymorphisms and pain sensitivity in this group.

METHODS

The cold pressor pain responses of 148 opioid dependent patients receiving MMT were evaluated using the cold pressor test (CPT). DNA was extracted from whole blood and subjected to polymerase chain reaction (PCR)-genotyping.

RESULTS

Of the 148 subjects, 77 (52.0%) were carriers of CYP2B6*6 allele. CYP2B6*6 allele carriers had shorter cold pain threshold and pain tolerance times than non-carriers of CYP2B6*6 allele (21.05s vs 33.69s, p=0.036 and 27.15s vs 44.51s, p=0.020, respectively). Pain intensity scores of the CYP2B6*6 allele carriers was 67.55, whereas that of the CYP2B6*6 allele non-carriers was 64.86 (p=0.352).

CONCLUSION

Our study indicates that the CYP2B6*6 allele is associated with a lower pain threshold and lower pain tolerance among males with opioid dependence on MMT. The CYP2B6*6 allele may provide a mechanistic explanation for clinical observations of heightened pain sensitivity among opioid dependent patients receiving MMT.

The AC/AG Diplotype for the 118A>G and IVS2 + 691G>C Polymorphisms of OPRM1 Gene is Associated with Sleep Quality Among Opioid-Dependent Patients on Methadone Maintenance Therapy

Introduction

Methadone is a full agonist of the opioid receptor mu 1 which is encoded by the OPRM1 gene. Sleep disorders were frequently reported by opioid-dependent patients during methadone maintenance therapy (MMT). It is possible, therefore, that genetic polymorphisms in OPRM1 influence sleep quality among patients on MMT. This study investigated the association of OPRM1 polymorphisms with sleep quality among opioid-dependent patients on MMT.

Methods

The sleep quality of 165 male opioid-dependent patients receiving MMT was evaluated using the Pittsburgh Sleep Quality Index (PSQI). DNA was extracted from whole blood and subjected to polymerase chain reaction (PCR) genotyping.

Results

Patients with IVS2 + 691 CC genotype had higher PSQI scores [mean (SD) = 5.73 (2.89)] compared to those without the IVS2 + 691 CC genotype (IVS2 + 691 GG/GC genotype) [4.92 (2.31)], but the difference did not reach statistical significance (p = 0.081). Patients with combined 118 AA genotype and IVS2 + 691 GC genotype (AC/AG diplotype) had significantly lower PSQI scores [mean (SD) = 4.25 (2.27)] compared to those without the diplotype [5.68 (2.77)] (p = 0.018).

Conclusion

Our study indicates that the AC/AG diplotype for the 118A>G and IVS2 + 691G>C polymorphisms of OPRM1 gene is associated with better sleep quality among males with opioid dependence on MMT.